In recent years, braking force has been increased due to disc brake spread. Contrary to this, sometimes uncomfortable low frequency noise, especially during traveling, is caused due to vibration of the brake rotor sandwiched between the brake pads. Such a phenomenon called “brake judder” has been noticed in development of high performance vehicle with less noise. Thus, it is a new technical object to analyze and improve the brake judder problem.
Although the mechanism which causes brake judder has not been clearly solved, it is believed that the accuracy of surface run-out of the brake rotor contacting the brake pads is one cause of brake judder. The accuracy of surface run-out of the brake rotor is influenced not only by the run-out accuracy of the brake rotor itself, but by accuracy of the surface run-out of the wheel mounting flange; axial run-out of the rolling bearing; accuracy of the raceway surfaces; and assembling accuracy of the rolling bearing; etc.
Recently in vehicle wheel bearing apparatus design, it is desired, on one hand, to reduce the weight and size, to reduce manufacturing cost and fuel consumption. On the other hand, there is a desire to increase rigidity to improve steering stability. Thus, the run-out accuracy of the brake rotor has to be solved to satisfy both matters which are contrary to one another.
FIG. 4 shows a vehicle wheel bearing apparatus. FIG. 4(a) is a side elevation view and FIG. 4(b) is its longitudinal cross-section view. In the description below, the term “outboard side” (a left-hand side in drawings) of the apparatus denotes a side which is positioned outside of the vehicle body. The term “inboard side” (a right-hand side in drawings) of the apparatus denotes a side which is positioned inside of the body when the bearing apparatus is mounted on the vehicle body.
This bearing apparatus has an inner member 51 with a wheel hub 52 and an inner ring 53. The wheel hub 52 has, at one end, an integrally formed wheel mounting flange 55 to mount a wheel (not shown) at the outboard side. An inner raceway surface 52a is formed on the outer circumferential surface of the wheel hub 52. An axially extending portion, of smaller diameter, extends from the inner raceway surface 52a. An inner ring 53 is press-fit onto the axially extending portion 54 of the wheel hub 52 to form an inner raceway surface 53a on the outer circumferential surface of the wheel hub. An outer member 60 is integrally formed with a body mounting flange 61 on its outer circumferential surface. The flange 61 is to be mounted on a body (not shown) of the vehicle. Double row raceway surfaces 60a, 60b are formed on its inner circumferential surface. Double row rolling elements (balls) 63, 63 are rollably held by cage 62 between the outer and inner raceway surfaces. Hub bolts 56, to secure a wheel on the flange, are arranged equidistantly along the circumference of the wheel mounting flange 55.
Seals 64, 65 are arranged at the ends of the outer member 60 to seal an annular space between the outer member 60 and the inner member 51. The seals 64, 65 prevent leakage of grease contained within the bearing as well as ingress of rain water or dust from the outside.
An annular groove 57 is formed on a side surface 55a of the wheel mounting flange 55 by a primary cut with a lathe. Bolt apertures 58 are equidistantly arranged in the annular groove 57 at substantially the middle of the width of the annular groove 57. The side surface 55a is finished by a secondary cut, e.g. with a lathe, after a knurled portion 56a of each hub bolt 56 has been press-fit into the bolt aperture 58.
In such a vehicle wheel bearing apparatus of the prior art, since the annular groove 57 is formed on the side surface 55a, it is possible to minimally limit influence due to deformation of the side surface 55a caused by the press-fit of the hub bolts 56. In addition, since the side surface 55a is finished by a secondary cut after press-fitting of the hub bolts 56, the surface run-out increased by the press-fit of the hub bolts can be substantially reduced. For example, see Japanese Laid-open Patent Publication No. 154801/2003.